ARM: support XZ compressed kernels

Wire up support for the XZ decompressor

Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
arch/arm/boot/compressed/string.c: remove memmove duplicate

Signed-off-by: faux123 <reioux@gmail.com>
gitignore: updated to exclude xz kernel files

and other user define files

Signed-off-by: faux123 <reioux@gmail.com>